The proposed research program involves the definition and analysis of the behavioral characteristics of five mammalian species (lion tamarin, rufous elephant shrew, bush dog, crab-eating fox, maned wolf) exhibiting graduations in monogamy. A major goal is the determination of whether life history characteristics and the type of monogamy are predictably correlated. The species will be compared with respect to pair-bond strength through the observation of the agonistic and affiliative interactions of mated pairs during and after pair-bond formation, and during reproduction. The degree of sex-specific aggression will be examined. Sex differences in roles will be compared in the five species, especially male and female parental investment and territorial behavior, e.g., scent-marking. Parental tolerance towards maturing offspring will be tested by the establishment of nuclear families, and the contribution of older juvenile helpers to rearing younger siblings will be determined. The relative importance of parental aggression or within-sibling aggression in promoting dispersal will be investigated. This study will be a test of recent evolutionary theory and will contribute to our understanding of the evolution of monogamy and the nuclear family as a reproductive strategy.